90 



CHAPTER IV. 



FRESH-WATER FISHES OF THE ORDER PHYSOSTOMI. 



FAMILY SILURID^E GENUS SILURUS- FAMILY CYPRINID.E GENUS CYPRINUS : The 

 Carp: Its Varieties and Hybrids GENUS CARASSIUS : The Crucian Carp Goldfish The 

 Carassius Bucephalus GEN is BAHBUS : The Barbels of Central Europe and Spain GENUS 

 AULOPYGE : Aulopyge hugelii GENUS GOBIO : The Gudgeon Gobio uranoscopus. 



FAMILY: SILURID^E. 

 GENUS: SiluruS (LiNN^us). 



THE great family of Siluroid fishes is characterised by having the skin 

 naked, or armoured with bony scutes, but scales are not developed. The 

 margin of the upper jaw is formed by the pre-maxillary bone, and the 

 maxillary bone is usually a rudiment, which forms the base for a maxillary 

 barbel. Barbels are always present. The sub-ope rcular bone is always want- 

 ing. The air-bladder generally communicates with the organ of hearing by 

 auditory ossicles. 



Dr. Giinther remarks that in the typical Siluroids the cranial cavity is 

 closed at the sides, as in the Cyprinidte, by the orbito-sphenoid and ethmoid 

 bones, which unite with the pre-frontal bones. The supra-occipital bone is 

 greatly developed, and many Siluroids have the skull enlarged posteriorly by a 

 kind of helmet formed of dermal ossifications, which spread over the region of 

 the neck. 



As a rule, there is a strong dorsal spine, which is articulated to a buckler 

 formed of the second and third inter-neural bones. 



The Siluroids have been separated by Giinther into eight great groups, 

 distinguished by the relative length, development, and position of the dorsal 

 and anal fins, the gill-membranes, the barbels, the nostrils, and the vent. 

 These sub-families are named Homalopteree , Heteroptera, Anomaloptera , 

 Proteroptera, Stenobranchia, Proteropodes, Opisthopterae, and Branckicola. 



The genus Silurus is included in the Heteroptera, which have the dorsal 

 fin very short, the anal fin elongated, the ventral fins below or behind the 

 dorsal, and the caudal fin rounded. Nearly all Siluroid fishes, which include 

 fully one hundred and twenty genera, characterise fresh waters, though some 

 enter the sea. They are most numerous in the Tropics. 



